Abstract: In the context of climate change and possible responses to the risk associated with it, three variables strongly influence the levels and growth of greenhouse gas emissions: population, income (measured as per capita gross domestic product [GDP]), and intensity of emissions (measured as tons of greenhouse gas emissions per million dollars of GDP).
(Population) x (per capita GDP) x (Intensityghg) = Emissionsghg
This is the relationship for a given point in time; over time, any effort to change emissions alters the exponential rates of change of these variables. This means that the rates of change of the three left-hand variables, measured in percentage of annual change, sum to the rate of change of the right-hand variable, emissions.

For most countries, and for the world as a whole, population and per capita GDP are rising faster than intensity is declining, so emissions are rising.

Within this generalization, countries vary widely. During the 1990s, in some countries, including India, Japan, Brazil, Canada, Mexico, South Korea, Indonesia, and South Africa, population growth alone exceeded the decline in intensity. For China, India, Brazil, Mexico, Indonesia, and South Korea, population growth exceeding 1% per year combined with per capita GDP growth that exceeded the intensity improvement each achieved. For the United States, Canada, and Australia, income growth alone exceeded the decline in intensity. Yet several developed countries improved their per capita GDP while decreasing their emissions: Germany, the United Kingdom, France, and Poland; each did so by combining slow population growth (0.4% or less per year) with substantial improvements in intensity (-2.5% or better per year).

Stabilizing greenhouse gas emissions would mean the rate of change equals zero. Globally, with a population growth rate of 1.4% per year and an income growth rate of 1.7% per year, intensity would have to decline at a rate of -3.1% per year to hold emissions at the level of the year that rate of decline went into effect. Within the United States, at the 1990s population growth rate of 1.2% per year and income growth rate of 1.8% per year, intensity would have had to decline at a rate of -3.0% per year to hold emissions level; however, U.S. intensity declined at a rate of -1.6%, leaving emissions to grow at 1.4% per year. President Bush’s Climate Change Initiative seeks to increase the rate of intensity decline through 2012 by about -0.4% per year — well short of stabilizing or reducing greenhouse gas emissions.
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Topics: Climate Change, Energy, Population